Electromechanical actuators are used in a wide range of technology, for actuating system parts, for example in engine, machine, vehicle or aviation technology.
An electromechanical actuator is driven by an AC motor comprising a stator assembly and a rotor.
For some EMA applications such as flight control actuation, landing gear actuation, steering actuation, safety reasons imply that the motor shall oppose a drag torque, proportional to the revolution speed, in case the electric supply fails. This function is called damping function.
Most conventional electric motors have stator cores constructed from sheets of laminated iron alloy, as shown in FIG. 1. Individual laminations are punched from flat sheets of iron alloy using specially constructed dies with the necessary shape and with slots and teeth incorporated into them. Laminations made by this method are generally coated with a thin insulation layer and are then stacked together to form the laminated stator. It is important that the laminations are stacked in correct alignment and secured together for example by welding. The use of thin laminations prevents induced currents and losses that can adversely affect motor operation.
An alternative, but less widely-used, construction of a stator core involves the use of specially formed iron powder particles pressed into a mold to form the appropriate shape. To avoid losses and to prevent induced currents, special iron particles have to be used, for example iron powder coated with a thermal plastic material and comprising a phosphate layer.
In addition, regardless of which of these methods is used, it is necessary to provide additional componentry to the stator if damping of the motor is required.
Existing systems use additional, or add-on damping devices to provide the required damping. These do, however, have significant negative impact on the overall volume and size of the motor.
The aim of the present invention is to provide a stator that provides effective damping without substantially increasing the volume of the motor.
As mentioned above, in the existing, conventional systems, steps are taken, conventionally by the use of laminations, or, otherwise, by using special powder compositions, to avoid or prevent induced currents.